Heat oil in a large pot over medium heat. Add onion and garlic and saute for 2-3 minutes. Season with salt and pepper.
Add sweet potatoes, vegetable broth and water. Bring to a boil and then reduce the heat to low.
Simmer, covered for 20 minutes or until sweet potatoes are tender.
Using an immersion blender, puree soup until smooth and creamy. (NOTE: If you don't have an immersion blender, transfer soup, in batches, to a regular blender and blend until smooth.)
Add peanut butter and chili garlic sauce to the pan and continue pureeing with the immersion blender.
Top with chopped peanuts and chopped cilantro before servings.